It is now commonly acknowledged that learning disabled
children are not a homogeneous population, and current
neuropsychological research in this area has focussed on
attempts to identify subtypes of these disorders. Earlier
subtyping studies adopted a subjective, clinical-inferential
approach to classification, while recent research has
emphasised a strictly objective, quantitative model which
involves the use of multivariate statistical methods of
classification. In the natural sciences, both objective
quantification as well as the developmental, qualitative
aspects of taxonomy are considered equally essential for a
good classification (Adams,1985). Subtypes identified so far
in various studies have had relatively little impact on
either neuropsychological theory or clinical practice, and
this has been attributed to a failure on the part of
researchers to integrate the clinical-qualitative approach
with the quantitative subtyping procedures (Wilson &
Risucci,1986).
The present study attempted to address this problem by
using a combination of these two generally accepted methods,
in an attempt to identify reliable and meaningful subtypes
within a sample of 275 clinic-referred and 26 normal control
subjects. Two separate typologies of this subject sample were
generated: a) using clinical-inferential methods, based on
clinical inspection of psychometric test data, and b) using
multivariate statistical methods for the derivation of
subtypes (cluster analysis). The two subtyping solutions were
then compared, allowing each to be used to validate the other
(Morris & Satz,1984).
The derived clusters and clinical typology groups
identified all commonly found subtypes as well as most others
reported by previous subtyping studies in the literature. The
results of several internal validation procedures indicated
that the clusters were relatively heterogeneous, and
therefore somewhat unreliable, although the majority of
clusters proved to be meaningful and interpretable.
Comparison of the two classifications indicated approximately
58% correspondence in terms of individual case assignments to
comparable subtypes between the typologies. Comparison of
T-score ability profiles revealed generally satisfactory
correspondence between the profiles of cluster analysis
derived subtypes and those of comparable clinical subtypes.
Further analyses were performed on selected groups of
subjects in order to explore specific hypotheses. Age effects
on subtype patterns were examined, and the results suggested
that subtypes do persist over the school age range. However,
adolescent subjects were more prominent in the severe
language disorder subtypes, and a large proportion of the
younger subjects emerged in subtypes characterized by visual
perceptual problems. Reading disability subtypes were also
analysed, indicating qualified support for Denckla's (1977)
subtypes from the cluster analysis, but considerable
confirmation of this typology from the clinical
classification. Rourke and Finlayson's (1978) findings in
regard to specific arithmetic disabilities were not
replicated in this study. Subjects with specific profile
patterns were also examined for evidence of characteristic
social, emotional and behavioural difficulties, with mixed
results. Finally, the obtained subtypes were examined in
order to determine possible differences in terms of academic
performance, in order to establish external validity for the
two classifications.
It was concluded that, although there are definable as
well as meaningful subtypes of learning disabilities, this
population of children cannot be classified into discrete
subtypes with clear boundaries and strictly defined criteria.
In addition, it was deemed important to recognize that such
disorders range, in degree of severity, from quite subtle to
seriously impaired, so that diagnostic "cut off" points are
inappropriate for this particular group of children. / Graduate
| Identifer | oai:union.ndltd.org:uvic.ca/oai:dspace.library.uvic.ca:1828/9501 |
| Date | 22 June 2018 |
| Creators | Peter, Barbara Mary |
| Contributors | Spreen, Otfried |
| Source Sets | University of Victoria |
| Language | English, English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
| Rights | Available to the World Wide Web |
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